1. Field of the Invention
The present invention relates to a method of forming a resist pattern and to an exposure device, and in particular, to a method of forming a resist pattern and an exposure device which are based on an exposure technique using a KrF excimer laser as a light source in the production of a semiconductor integrated circuit.
2. Description of the Related Art
Conventionally, in manufacturing a semiconductor integrated circuit, in order to form a finer pattern, a KrF exposure technique has been mainly used, in which deep UV light having a wavelength of 248 nm is emitted as exposure light from a KrF excimer laser light source. In this KrF exposure technique, it is possible to form a patter of about 0.2 xcexcm.
Japanese Patent Application Laid-Open (JP-A) No. 11-119443 discloses, in such a KrF exposure technique, a technique in which a fine pattern of about 0.2 xcexcm or less is obtained by shrinking the resist pattern (e.g., shrinking the internal diameter of the hole pattern formed at the resist) by baking the resist at a temperature which is higher than the usual baking which is carried out in order to remove the residual solvent and the residual moisture which remain after the resist pattern has been formed. In accordance with this technique, it is possible to form a pattern of about 0.1 xcexcm or less, which exceeds the resolution limit of the KrF exposure technique.
The method disclosed in the aforementioned JP-A-11-119443 is suited to the formation of an extremely fine pattern for which the size (dimension) of a feature (e.g., the diameter of a contact hole, the width of an embedded wiring, or the like) is less than or equal to the resolution limit of the KrF exposure technique. However, for a relatively large pattern whose feature dimension is greater than the resolution limit of the KrF exposure technique, the pattern after baking deteriorates, and thus, this method is not preferable.
For example, as illustrated in FIG. 10A, when holes (a contact hole pattern) of a diameter of about 0.25 xcexcm and holes (a contact hole pattern) of a diameter of about 0.5 xcexcm are formed in a resist and the resist is baked for 60 seconds at around 135xc2x0 C., as illustrated in FIG. 10B, the side walls at the holes (the contact hole pattern) of a diameter of about 0.25 xcexcm do not deform and only the diameter decreases such that holes of a diameter of about 0.1 xcexcm are formed. However, at the holes (the contact hole pattern) having a diameter of about 0.5 xcexcm, the resist side walls forming the pattern curve towards the centers of the holes, such that deformed holes whose smallest diameter is 0.35 xcexcm are formed.
When a resist having holes of such configurations is used as a mask in the etching process which is carried out later, the portions corresponding to the peaks of the convex shapes of the resist are gradually removed as the film to be processed, which is the layer therebeneath, is etched. In addition, the resist side walls are curved toward the centers of the holes and the smallest diameter thereat is 0.35 xcexcm. Therefore, considering that the diameter of the bottom surface of the hole which is nearer to the surface of the film to be processed is greater than 0.35 xcexcm and that the film to be processed can be somewhat side-etched at the border region at the time of etching, a hole of a diameter much larger than the desired diameter is formed in the film to be processed. This tendency becomes marked particularly when the diameter of the resist pattern before baking is greater than 0.5 xcexcm.
In view of the aforementioned, an object of the present invention is to provide a method of forming a resist pattern in which a relatively large pattern, whose feature dimension is greater than the resolution limit of the KrF exposure technique, and an extremely fine pattern, whose feature dimension is less than or equal to the resolution limit of the KrF exposure technique, can be formed well simultaneously.
In order to achieve the above object, an aspect of the present invention is a method for forming a resist pattern including the steps of: subjecting a resist, which is applied on a surface of an object to be processed, to pattern exposure in which a first exposure amount for forming a pattern is applied to the resist; forming a resist pattern by developing the resist; subjecting the resist pattern to a second exposure in which a second exposure amount, which adjusts a shrinkage rate of the resist pattern, is applied to the resist pattern; and subjecting the resist to a bake process at a temperature at which the resist flows.
Namely, for a resist pattern formed on an object to be processed, the heat resistance of the resist is changed by carrying out an exposure which applies a second exposure amount. The heat resistance of the resist affects the shrinkage rate of the resist pattern at the time of high temperature bake processing. The greater the heat resistance, the lower the shrinkage rate. Because the heat resistance of the resist varies in accordance with the second exposure amount, in the first aspect of the present invention, the shrinkage rate of the resist pattern at the time of high temperature bake processing is adjusted by adjusting the second exposure amount.
Namely, a heat resistance of the resist is desired which is such that the shrinkage rate of the resist pattern is a predetermined shrinkage rate. By applying the amount of exposure, which results in this heat resistance, as the second exposure amount, the shrinkage rate of the resist pattern is adjusted, and the resist pattern can be shrunk to a desired dimension.
Control may be carried out such that second exposure amount is applied to the resist pattern at the regions to be shrunk and the shrinkage rate of the resist pattern is adjusted such that the resist pattern is shrunk to a desired dimension. Conversely, control may be carried out such that the second exposure amount is applied to the resist pattern at the regions to be shrunk such that shrinkage of the resist pattern is suppressed.